Aug. 13, 2010 -- Building muscle doesn't require a lot of heavy lifting, just a lot of light weight lifting, a new study indicates.

Straining to lift very heavy weights isn't the only way to pump up muscles, say researchers at McMaster University in Hamilton, Ontario. Similar results can be achieved, they say, by lifting light weights a greater number of times.

"Rather than grunting and straining to lift heavy weights, you can grab something much lighter but you have to lift it until you can't lift it any more," Phillips says in a news release.

The Study Method

Researchers recruited 15 healthy men with an average age of 21. Each was told to lift light weights and heavy weights with varying repetitions.

The weights represented a percentage of their best or heaviest lift. Heavier weights were set to 90% of a man's best lift, and light weights at 30%.

Phillips says weights set to 80% to 90% of a person's best lift required five to 10 repetitions before fatigue set in. At 30%, it took at least 24 lifts before similar fatigue developed.

The researchers measured fatigue at the cellular level by examining results of muscle biopsies done 4 hours and 24 hours after workouts.

Similar amounts of protein used in muscle building were produced whether volunteers lifted at 90% of their maximums until they ran out of steam and when they lifted only 30% of their best until they could lift no more, the researchers say.

Straining Not Necessary

In short, the authors say, similar muscle mass can be built by using light weights as with heavier ones.

"We're convinced that growing muscle means stimulating your muscle to make new muscle proteins, a process in the body that over time accumulates into bigger muscles," Phillips says. "We're excited to see where this new paradigm will lead."

What It Means

The research has practical significance, and not just for body builders, because building muscle is important for people with compromised skeletal muscle mass, such as the elderly, cancer patients, or people recovering from trauma, surgery, or even stroke, the researchers conclude.

They didn't measure actual muscle growth, relying instead for their conclusions on the cellular markers.

But the findings are nevertheless promising and need to be replicated in future research, the authors write.

Nicholas Burd, a PhD student and author of the study, and his colleagues, write that a "high-volume low-load resistance exercise" program may help reduce loss of muscle tissue that occurs as part of the natural aging process.

Lifting Lighter Weights Is Safer

At the same time, lifting lighter weights many times may reduce soft tissue and orthopaedic injury, the study says.

The findings suggest that low-load lifts performed with numerous repetitions or high-load muscle-stretching efforts "will result in similar training-induced" muscle growth, "or even superior gains," the authors write.